This invention relates to an acoustic filter used in telephone handset earpieces.
A telephone handset earpiece often includes a speaker, a protective cover with apertures to couple sound to a phone user""s ear, and an air-filled cavity between the speaker and the protective cover.
A phone user with normal hearing has no trouble hearing high frequency sounds but may have a problem with noise or hiss associated with the high frequency. A phone user with impaired hearing, on the other hand, often requires emphasis or amplification of high frequency components in audio signals.
The system described herein obviates the above described problems by providing a mechanically adjustable acoustic filter for a telephone handset earpiece that can be adjusted for users with normal hearing or for hearing-impaired users.
In one aspect, the disclosure features a mechanical acoustic filter having an enclosure and at least two plates within the enclosure. Each plate has a plurality of holes of a particular diameter. The two plates are capable of being displaced relative to each other, such that an aggregate size of the holes vary as the plates are displaced. The variations in the aggregate size of the holes within the enclosure changes the frequency response of the acoustic filter.
In some embodiments, the plates are substantially circular in shape and are displaced relative to each other by rotating the plates about a fixed pivot point. In other embodiments, the plates are disposed parallel to each other and are substantially rectangular or square in shape. The plates are displaced relative to each other by sliding the plates along the parallel direction.
In another aspect, the disclosure features a telephone handset having a housing, a speaker and communication electronics disposed within the housing, and a mechanical acoustic filter disposed on top of the speaker.
Advantages of using a mechanical acoustic filter compared to a typical electronic filter for an adjustable high-frequency cut-off include lower cost and less maintenance.